Hybrid power converter

ABSTRACT

A method includes configuring a hybrid converter to operate in a hybrid mode comprising four operating phases in response to an input voltage of the hybrid converter greater than a first threshold, configuring the hybrid converter to operate in a buck mode comprising two operating phases in response to the input voltage of the hybrid converter less than a second threshold, and configuring the hybrid converter to operate in a charge pump mode comprising two operating phases in response to the input voltage of the hybrid converter less than the first threshold and greater than the second threshold.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/133,101 entitled “Hybrid Power Converter” and filed on Sep. 17, 2018,which claims priority to U.S. Provisional Application Ser. No.62/649,756, entitled “Hybrid Power Converter” and filed on Mar. 29,2018, each application is hereby incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a hybrid power converter, and, inparticular embodiments, to a hybrid power converter in a receiver of awireless power transfer system.

BACKGROUND

As technologies further advance, wireless power transfer has emerged asan efficient and convenient mechanism for powering or charging batterybased mobile devices such as mobile phones, tablet PCs, digital cameras,MP3 players and/or the like. A wireless power transfer system typicallycomprises a primary side transmitter and a secondary side receiver. Theprimary side transmitter is magnetically coupled to the secondary sidereceiver through a magnetic coupling. The magnetic coupling may beimplemented as a loosely coupled transformer having a primary side coilformed in the primary side transmitter and a secondary side coil formedin the secondary side receiver.

The primary side transmitter may comprise a power conversion unit suchas a primary side of a power converter. The power conversion unit iscoupled to a power source and is capable of converting electrical powerto wireless power signals. The secondary side receiver is able toreceive the wireless power signals through the loosely coupledtransformer and convert the received wireless power signals toelectrical power suitable for a load.

As the power of the wireless power transfer system goes higher, theremay be a need for achieving a high-efficiency wireless power transferbetween the transmitter and the receiver. More particularly, achieving ahigh efficiency wireless power transfer under various input and outputconditions (e.g., different load currents and/or different rated inputvoltages of the receiver) has become a significant issue, which presentschallenges to the system design of the wireless power transfer system.

It would be desirable to have a high performance power receiverexhibiting good behaviors such as high efficiency under a variety ofinput and output conditions.

SUMMARY

These and other problems are generally solved or circumvented, andtechnical advantages are generally achieved, by preferred embodiments ofthe present disclosure which provide a hybrid power converter in areceiver of a wireless power transfer system.

In accordance with an embodiment, a method comprises configuring ahybrid converter to operate in a hybrid mode comprising four operatingphases in response to an input voltage of the hybrid converter greaterthan a first threshold, configuring the hybrid converter to operate in abuck mode comprising two operating phases in response to the inputvoltage of the hybrid converter less than a second threshold, andconfiguring the hybrid converter to operate in a charge pump modecomprising two operating phases in response to the input voltage of thehybrid converter less than the first threshold and greater than thesecond threshold.

In accordance with another embodiment, a method comprises detecting aninput voltage and an output voltage of a power system comprising ahybrid converter, configuring the hybrid converter to operate in ahybrid mode comprising four operating phases when the input voltage ofthe hybrid converter is greater than a first threshold, configuring thehybrid converter to operate in a buck mode comprising two operatingphases when the input voltage of the hybrid converter is less than asecond threshold, and configuring the hybrid converter to operate in acharge pump mode comprising two operating phases when the input voltageof the hybrid converter is between the first threshold and the secondthreshold.

An advantage of an embodiment of the present disclosure is a hybridpower converter in a receiver of a wireless power transfer systemoperates in the hybrid mode and charge pump mode to achieve highefficiency. Furthermore, a combination of the hybrid mode, the chargepump mode and the buck mode helps to provide flexibility in differentoperation conditions.

The foregoing has outlined rather broadly the features and technicaladvantages of the present disclosure in order that the detaileddescription of the disclosure that follows may be better understood.Additional features and advantages of the disclosure will be describedhereinafter which form the subject of the claims of the disclosure. Itshould be appreciated by those skilled in the art that the conceptionand specific embodiment disclosed may be readily utilized as a basis formodifying or designing other structures or processes for carrying outthe same purposes of the present disclosure. It should also be realizedby those skilled in the art that such equivalent constructions do notdepart from the spirit and scope of the disclosure as set forth in theappended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 illustrates a block diagram of a wireless power transfer systemin accordance with various embodiments of the present disclosure;

FIG. 2 illustrates a schematic diagram of the hybrid converter inaccordance with various embodiments of the present disclosure;

FIG. 3 illustrates the operating principle of the first phase of thehybrid mode in accordance with various embodiments of the presentdisclosure;

FIG. 4 illustrates the operating principle of the second phase of thehybrid mode in accordance with various embodiments of the presentdisclosure;

FIG. 5 illustrates the operating principle of the third phase of thehybrid mode in accordance with various embodiments of the presentdisclosure;

FIG. 6 illustrates the operating principle of the fourth phase of thehybrid mode in accordance with various embodiments of the presentdisclosure;

FIG. 7 illustrates the operating principle of the first phase of thecharge pump mode in accordance with various embodiments of the presentdisclosure;

FIG. 8 illustrates the operating principle of the second phase of thecharge pump mode in accordance with various embodiments of the presentdisclosure;

FIG. 9 illustrates the operating principle of the first phase of thebuck mode in accordance with various embodiments of the presentdisclosure;

FIG. 10 illustrates the operating principle of the second phase of thebuck mode in accordance with various embodiments of the presentdisclosure;

FIG. 11 illustrates the operating principle of the first phase of thehybrid converter operating in both the buck mode and the auto mode inaccordance with various embodiments of the present disclosure;

FIG. 12 illustrates the operating principle of the second phase of thehybrid converter operating in both the buck mode and the auto mode inaccordance with various embodiments of the present disclosure;

FIG. 13 illustrates the operating principle of the auto mode inaccordance with various embodiments of the present disclosure;

FIG. 14 illustrates the mode transition principle in accordance withvarious embodiments of the present disclosure;

FIG. 15 illustrates a flow chart of applying a first control mechanismto the hybrid converter shown in FIG. 2 in accordance with variousembodiments of the present disclosure;

FIG. 16 illustrates a flow chart of applying a second control mechanismto the hybrid converter shown in FIG. 2 in accordance with variousembodiments of the present disclosure;

FIG. 17 illustrates a flow chart of applying a third control mechanismto the hybrid converter shown in FIG. 2 in accordance with variousembodiments of the present disclosure; and

FIG. 18 illustrates a flow chart of applying a fourth control mechanismto the hybrid converter shown in FIG. 2 in accordance with variousembodiments of the present disclosure.

Corresponding numerals and symbols in the different figures generallyrefer to corresponding parts unless otherwise indicated. The figures aredrawn to clearly illustrate the relevant aspects of the variousembodiments and are not necessarily drawn to scale.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the presently preferred embodiments arediscussed in detail below. It should be appreciated, however, that thepresent disclosure provides many applicable inventive concepts that canbe embodied in a wide variety of specific contexts. The specificembodiments discussed are merely illustrative of specific ways to makeand use the disclosure, and do not limit the scope of the disclosure.

The present disclosure will be described with respect to preferredembodiments in a specific context, namely a hybrid power converteroperating in different operating modes for increasing efficiency andperformance of wireless power transfer systems. The disclosure may alsobe applied, however, to a variety of power systems. Hereinafter, variousembodiments will be explained in detail with reference to theaccompanying drawings.

FIG. 1 illustrates a block diagram of a wireless power transfer systemin accordance with various embodiments of the present disclosure. Thewireless power transfer system 100 comprises a power converter 104 and awireless power transfer device 101 connected in cascade between an inputpower source 102 and a load 114. In some embodiments, the powerconverter 104 is employed to further improve the performance of thewireless power transfer system 100. In alternative embodiments, thepower converter 104 is an optional element. In other words, the wirelesspower transfer device 101 may be connected to the input power source 102directly.

The wireless power transfer device 101 includes a power transmitter 110and a power receiver 120. As shown in FIG. 1, the power transmitter 110comprises a transmitter circuit 107 and a transmitter coil L1 connectedin cascade. The input of the transmitter circuit 107 is coupled to anoutput of the power converter 104. The power receiver 120 comprises areceiver coil L2, a resonant capacitor Cs, a rectifier 112 and a hybridconverter 113 connected in cascade. As shown in FIG. 1, the resonantcapacitor Cs is connected in series with the receiver coil L2 andfurther connected to the inputs of the rectifier 112. The outputs of therectifier 112 are connected to the inputs of the hybrid converter 113.The outputs of the hybrid converter 113 are coupled to the load 114.

The power transmitter 110 is magnetically coupled to the power receiver120 through a magnetic field when the power receiver 120 is placed nearthe power transmitter 110. A loosely coupled transformer 115 is formedby the transmitter coil L1, which is part of the power transmitter 110,and the receiver coil L2, which is part of the power receiver 120. As aresult, electrical power may be transferred from the power transmitter110 to the power receiver 120.

In some embodiments, the power transmitter 110 may be inside a chargingpad. The transmitter coil L1 is placed underneath the top surface of thecharging pad. The power receiver 120 may be embedded in a mobile phone.When the mobile phone is place near the charging pad, a magneticcoupling may be established between the transmitter coil L1 and thereceiver coil L2. In other words, the transmitter coil L1 and thereceiver coil L2 may form a loosely coupled transformer through which apower transfer occurs between the power transmitter 110 and the powerreceiver 120. The strength of coupling between the transmitter coil L1and the receiver coil L2 is quantified by the coupling coefficient k. Insome embodiments, k is in a range from about 0.05 to about 0.9.

In some embodiments, after the magnetic coupling has been establishedbetween the transmitter coil L1 and the receiver coil L2, the powertransmitter 110 and the power receiver 120 may form a power systemthrough which power is wirelessly transferred from the input powersource 102 to the load 114.

The input power source 102 may be a power adapter converting a utilityline voltage to a direct-current (dc) voltage. Alternatively, the inputpower source 102 may be a renewable power source such as a solar panelarray. Furthermore, the input power source 102 may be any suitableenergy storage devices such as rechargeable batteries, fuel cells, anycombinations thereof and/or the like.

The load 114 represents the power consumed by the mobile device (e.g., amobile phone) coupled to the power receiver 120. Alternatively, the load114 may refer to a rechargeable battery and/or batteries connected inseries/parallel, and coupled to the output of the power receiver 120.Furthermore, the load 114 may be a downstream power converter such as abattery charger.

The transmitter circuit 107 may comprise primary side switches of afull-bridge converter according to some embodiments. Alternatively, thetransmitter circuit 107 may comprise the primary side switches of anyother suitable power converters such as a half-bridge converter, apush-pull converter, any combinations thereof and/or the like.

It should be noted that the power converters described above are merelyexamples. One having ordinary skill in the art will recognize othersuitable power converters such as class E topology based powerconverters (e.g., a class E amplifier), may alternatively be useddepending on design needs and different applications.

The transmitter circuit 107 may further comprise a resonant capacitor(not shown). The resonant capacitor and the magnetic inductance of thetransmitter coil may form a resonant tank. Depending on design needs anddifferent applications, the resonant tank may further include a resonantinductor. In some embodiments, the resonant inductor may be implementedas an external inductor. In alternative embodiments, the resonantinductor may be implemented as a connection wire.

The power receiver 120 comprises the receiver coil L2 magneticallycoupled to the transmitter coil L1 after the power receiver 120 isplaced near the power transmitter 110. As a result, power may betransferred to the receiver coil and further delivered to the load 114through the rectifier 112. The power receiver 120 may comprise asecondary resonant capacitor Cs as shown in FIG. 1.

The rectifier 112 converts an alternating polarity waveform receivedfrom the output of the receiver coil L2 to a single polarity waveform.In some embodiments, the rectifier 112 comprises a full-wave diodebridge and an output capacitor. In alternative embodiments, thefull-wave diode bridge may be replaced by a full-wave bridge formed byswitching elements such as n-type metal oxide semiconductor (NMOS)transistors.

Furthermore, the rectifier 112 may be formed by other types ofcontrollable devices such as metal oxide semiconductor field effecttransistor (MOSFET) devices, bipolar junction transistor (BJT) devices,super junction transistor (SJT) devices, insulated gate bipolartransistor (IGBT) devices, gallium nitride (GaN) based power devicesand/or the like. The detailed operation and structure of the rectifier112 are well known in the art, and hence are not discussed herein.

The hybrid converter 113 is coupled between the rectifier 112 and theload 114. The hybrid converter 113 is a non-isolated power converter. Bycontrolling the on/off of the switches of the hybrid converter 113, thehybrid converter 113 can be configured as a buck converter, a chargepump converter or a hybrid converter.

Depending design needs and different applications, the hybrid converter113 may operate in different operating modes. More particularly, thehybrid converter 113 may operate in a buck mode when the load current isless than a predetermined current threshold and/or the input voltage isless than a predetermined voltage threshold. In the buck mode, thehybrid converter 113 is configured as a buck converter. The hybridconverter 113 may operate in a charge pump mode or a hybrid mode whenthe input voltage is greater than the predetermined voltage thresholdand/or the load current is greater than the predetermined currentthreshold. More particularly, in some embodiments, the hybrid converter113 may operate in a charge pump mode or a hybrid mode when a ratio ofthe output voltage of the hybrid converter to the input voltage of thehybrid converter is less than 0.5. In the charge pump mode, the hybridconverter 113 is configured as a charge pump converter. In the hybridmode, the hybrid converter 113 is configured as a hybrid converter.

The schematic diagram of the hybrid converter 113 will be describedbelow with respect to FIG. 2. The detailed configuration (e.g.,different operating modes and their corresponding converterconfigurations) of the hybrid converter 113 will be described below withrespect to FIGS. 3-12.

In some embodiments, the input voltage of the hybrid converter 113 is ina range from about 18 V to about 22 V. The output voltage of the hybridconverter 113 is about 9 V. One advantageous feature of having thehybrid converter 113 is that a higher output voltage (e.g., 22 V) can beachieved at the output of the rectifier 112. Such a higher outputvoltage helps to lower down the current flowing through the receivercoil L2, thereby improving the efficiency of the power receiver 120.

FIG. 2 illustrates a schematic diagram of the hybrid converter inaccordance with various embodiments of the present disclosure. Thehybrid converter 113 comprises a first switch Q1, a capacitor C_(CP), asecond switch Q2, a third switch Q3, a fourth switch Q4, an outputinductor Lo and an output capacitor Co. As shown in FIG. 2, the outputinductor Lo and the output capacitor Co form an output filter. The firstswitch Q1, the capacitor C_(CP) and the second switch Q2 are connectedin series between an input voltage source VIN and the output filter. Acommon node of the first switch Q1 and the capacitor C_(CP) is denotedas CP+ as shown in FIG. 2. Likewise, a common node of the second switchQ2 and the capacitor C_(CP) is denoted as CP−. A common node of thesecond switch Q2 and the output filter is denoted as VX. As shown inFIG. 2, the third switch Q3 is connected between CP+ and VX. The fourthswitch Q4 is connected between CP− and ground.

In some embodiments, the capacitor C_(CP) functions as a charge pumpcapacitor. Throughout the description, the capacitor C_(CP) isalternatively referred to as the charge pump capacitor C_(CP).

In accordance with an embodiment, the switches (e.g., switches Q1-Q4)may be metal oxide semiconductor field-effect transistor (MOSFET)devices. Alternatively, the switching element can be any controllableswitches such as insulated gate bipolar transistor (IGBT) devices,integrated gate commutated thyristor (IGCT) devices, gate turn-offthyristor (GTO) devices, silicon controlled rectifier (SCR) devices,junction gate field-effect transistor (JFET) devices, MOS controlledthyristor (MCT) devices and the like.

It should be noted while FIG. 2 shows the switches Q1-Q4 are implementedas single n-type transistors, a person skilled in the art wouldrecognize there may be many variations, modifications and alternatives.For example, depending on different applications and design needs, theswitches Q1-Q4 may be implemented as p-type transistors. Furthermore,each switch shown in FIG. 2 may be implemented as a plurality ofswitches connected in parallel. Moreover, a capacitor may be connectedin parallel with one switch to achieve zero voltage switching (ZVS)/zerocurrent switching (ZCS).

The hybrid converter 113 includes three different operating modes,namely a hybrid mode, a charge pump mode and a buck mode. In someembodiments, when the output power of the wireless power system supportsthe 5 W baseband power profile (BPP) and 5-15 W extended power profile(EPP), the hybrid converter 113 operates in the buck mode. When theoutput power of the wireless power system supports the 5-15 W BPP and15-20 W EPP, the hybrid converter 113 operates in either the hybrid modeor the charge pump mode. Furthermore, the hybrid converter 113 mayoperate in a mode combining the hybrid mode and the charge pump mode. Inother words, the hybrid converter 113 may have a mode transition betweenthe hybrid mode and the charge pump mode.

It should be noted that the power range used in the previous example areselected purely for demonstration purposes and are not intended to limitthe various embodiments of the present disclosure to any particularpower range.

In the hybrid mode, the hybrid converter 113 operates in four differentphases. In each phase, the current flowing through the output inductorLo may ramp up or down depending on different combinations of the inputvoltage V_(IN), the voltage across the charge pump capacitor C_(CP) andthe output voltage V_(OUT). In the hybrid mode, the voltage of thehybrid converter 113 can be regulated to a predetermined voltage. Sincethe hybrid converter 113 under the hybrid mode has tight voltageregulation, any loads (e.g., battery chargers) can be connected to theoutput of the hybrid converter 113. The detailed operating principles ofthe hybrid mode will be described below with respect to FIGS. 3-6.

In the charge pump mode, the hybrid converter 113 operates in twodifferent phases. In the charge pump mode, the voltage of the hybridconverter 113 is not regulated. Since the hybrid converter 113 under thecharge pump mode may vary in a wide range, only some loads (e.g.,battery chargers having good transient performance) can be connected tothe output of the hybrid converter 113. The detailed operatingprinciples of the charge pump mode will be described below with respectto FIGS. 7-8.

In the buck mode, the hybrid converter 113 operates in two differentphases. The second switch Q2 and the third switch Q3 are always-on. As aresult, the charge pump capacitor C_(CP) is shorted and not part of theoperation of the buck mode. In each phase, the current flowing throughthe output inductor Lo may ramp up or down depending on differentcombinations of the input voltage V_(IN) and the output voltage V_(OUT).The detailed operating principles of the buck mode will be describedbelow with respect to FIGS. 9-10. Furthermore, in order to have a smoothtransition between the buck mode and the charge pump mode, the hybridconverter 113 may operate in an auto mode. In the auto mode, the chargepump capacitor is floating when the buck mode is applicable to thehybrid converter 113. The detailed operating principles of the buck modeand the auto mode will be described below with respect to FIGS. 11-12.

In order to improve the performance of the wireless power transfersystem 100 shown in FIG. 1, the hybrid converter 113 may be configuredto operate in the hybrid mode. The hybrid mode includes four differentphases. FIGS. 3-6 illustrate the operating principles of the four phasesof the hybrid mode in accordance with various embodiments of the presentdisclosure.

FIG. 3 illustrates the operating principle of the first phase of thehybrid mode in accordance with various embodiments of the presentdisclosure. During the first phase of the hybrid mode, switch Q3 isturned off as indicated by the arrow placed on top of the symbol ofswitch Q3. Likewise, switch Q4 is turned off as indicated by the arrowplaced on top of the symbol of switch Q4. Since switches Q1 and Q2 areturned on as shown in FIG. 3, a conductive path is established asindicated by the dashed line 302. The conductive path is formed byswitch Q1, the charge pump capacitor C_(CP), switch Q2 and outputinductor Lo. The current flows from the input power source V_(IN) to theoutput voltage V_(OUT) through the conductive path shown in FIG. 3.

During the first phase of the hybrid mode, the charge pump capacitorC_(CP) is charged and energy is stored in the charge pump capacitorC_(CP) accordingly. The current flowing through the inductor Lo may rampup or down depending on the voltage applied across the inductor Lo. Insome embodiments, when the input voltage VIN is greater than the sum ofthe voltage across the charge pump capacitor C_(CP) and the outputvoltage V_(OUT), the current flowing through the inductor Lo ramps upand the energy stored in the inductor Lo increases accordingly. Thecurrent slope S of the inductor Lo satisfies the following equation:

$\begin{matrix}{S = \frac{V_{IN} - V_{CS} - V_{OUT}}{L_{O}}} & (1)\end{matrix}$where V_(CS) is the voltage across the charge pump capacitor C_(CP).

FIG. 4 illustrates the operating principle of the second phase of thehybrid mode in accordance with various embodiments of the presentdisclosure. During the second phase of the hybrid mode, switches Q1 andQ3 are turned off as indicated by the arrows placed on their symbols.Since switches Q2 and Q4 are turned on, a conductive path is establishedas indicated by the dashed line 402 shown in FIG. 4. The conductive pathis formed by switch Q4, switch Q2 and output inductor Lo. In someembodiments, switch Q4 provides a freewheeling path for the currentflowing through the output inductor Lo.

During the second phase of the hybrid mode, the charge pump capacitorC_(CP) is isolated by the turned-off switches Q1 and Q3. The currentflowing through the inductor Lo ramps down and the energy stored in theinductor Lo decreases accordingly. The current slope S of the inductorLo satisfies the following equation:

$\begin{matrix}{S = \frac{- V_{OUT}}{L_{O}}} & (2)\end{matrix}$

FIG. 5 illustrates the operating principle of the third phase of thehybrid mode in accordance with various embodiments of the presentdisclosure. During the third phase of the hybrid mode, switches Q1 andQ2 are turned off as indicated by the arrows placed on their symbols.Since switches Q3 and Q4 are turned on, a conductive path is establishedas indicated by the dashed line 502 shown in FIG. 5. The conductive pathis formed by switch Q4, the charge pump capacitor C_(CP), switch Q3 andoutput inductor Lo.

During the third phase of the hybrid mode, the current discharges thecharge pump capacitor C_(CP) and the energy stored in the charge pumpcapacitor C_(CP) decreases accordingly. In some embodiments, the currentflowing through the inductor Lo may ramp up and the energy stored in theinductor Lo increases accordingly. In the third phase of the hybridmode, the current slope S of the inductor Lo satisfies the followingequation:

$\begin{matrix}{S = \frac{V_{CS} - V_{OUT}}{L_{O}}} & (3)\end{matrix}$

FIG. 6 illustrates the operating principle of the fourth phase of thehybrid mode in accordance with various embodiments of the presentdisclosure. During the fourth phase of the hybrid mode, switches Q1 andQ3 are turned off as indicated by the arrows placed on their symbols.Since switches Q2 and Q4 are turned on, a conductive path is establishedas indicated by the dashed line 602 shown in FIG. 6. The conductive pathis formed by switch Q4, switch Q2 and output inductor Lo. In someembodiments, switch Q4 provides a freewheeling path for the currentflowing through the output inductor Lo.

During the fourth phase of the hybrid mode, the charge pump capacitorC_(CP) is isolated by the turned-off switches Q1 and Q3. The currentflowing through the inductor Lo ramps down and the energy stored in theinductor Lo decreases accordingly. In the fourth phase of the hybridmode, the current slope S of the inductor Lo satisfies the followingequation:

$\begin{matrix}{S = \frac{- V_{OUT}}{L_{O}}} & (4)\end{matrix}$

It should be noted during the hybrid mode, the hybrid converter 113 mayoperate in the four phases described above with respect to FIGS. 3-6.More particularly, the hybrid converter 113 may operate in the fourphases in a sequential order as indicated by the phase number. Inaddition, the operating time of each phase may be determined by acontroller (not shown). The controller detects various operatingparameters (e.g., input voltage, output voltage, load current, anycombinations thereof and the like). Based upon the detected operatingparameters, the controller sets up the operating time of each phase.

FIG. 7 illustrates the operating principle of the first phase of thecharge pump mode in accordance with various embodiments of the presentdisclosure. During the first phase of the charge pump mode, switch Q3 isturned off as indicated by the arrow placed on top of the symbol ofswitch Q3. Likewise, switch Q4 is turned off as indicated by the arrowplaced on top of the symbol of switch Q4. Since switches Q1 and Q2 areturned on, a conductive path is established as indicated by the dashedline 702 shown in FIG. 7. The conductive path is formed by switch Q1,the charge pump capacitor C_(CP), switch Q2 and output inductor Lo. Thecurrent flows from the input power source V_(IN) to the output voltageV_(OUT) through the conductive path shown in FIG. 7. During the firstphase of the charge pump mode, the charge pump capacitor C_(CP) ischarged and energy is stored in the charge pump capacitor C_(CP)accordingly.

FIG. 8 illustrates the operating principle of the second phase of thecharge pump mode in accordance with various embodiments of the presentdisclosure. During the second phase of the charge pump mode, switches Q1and Q2 are turned off as indicated by the arrows placed on theirsymbols. Since switches Q3 and Q4 are turned on, a conductive path isestablished as indicated by the dashed line 802 shown in FIG. 8. Theconductive path is formed by switch Q4, the charge pump capacitorC_(CP), switch Q3 and output inductor Lo. During the second phase of thecharge pump mode, the current discharges the charge pump capacitorC_(CP) and the energy stored in the charge pump capacitor C_(CP)decreases accordingly.

It should be noted during the charge pump mode, the output inductor Lois an optional element. Depending different applications and designneeds, the output inductor Lo may be removed for further reducing thecost of the hybrid converter 113.

FIG. 9 illustrates the operating principle of the first phase of thebuck mode in accordance with various embodiments of the presentdisclosure. During the buck mode, switches Q2 and Q3 are always on. Inthe first phase of the buck mode, switch Q4 is turned off as indicatedby the arrow placed on top of the symbol of switch Q4. Since switchesQ1, Q2 and Q3 are turned on, the charge pump capacitor C_(CP) is shoredby the turned-on switches Q2 and Q3, and a conductive path isestablished as indicated by the dashed line 902 shown in FIG. 9. Theconductive path is formed by switch Q1, switch Q3 and output inductorLo. The current flows from the input power source V_(IN) to the outputvoltage V_(OUT) through the conductive path shown in FIG. 9.

During the first phase of the buck mode, the current flowing through theinductor Lo ramps up and the energy stored in the inductor L increasesaccordingly. The current slope S of the inductor Lo satisfies thefollowing equation:

$\begin{matrix}{S = \frac{V_{IN} - V_{OUT}}{L_{O}}} & (5)\end{matrix}$

FIG. 10 illustrates the operating principle of the second phase of thebuck mode in accordance with various embodiments of the presentdisclosure. During the second phase of the charge pump mode, switch Q1is turned off as indicated by the arrow placed on its symbol. Aconductive path is established as indicated by the dashed line 1002shown in FIG. 10. The conductive path is formed by switch Q4, switch Q2and output inductor Lo.

During the second phase of the buck mode, the current flowing throughthe inductor Lo ramps down and the energy stored in the inductor Lodecreases accordingly. The current slope S of the inductor Lo satisfiesthe following equation:

$\begin{matrix}{S = \frac{- V_{OUT}}{L_{O}}} & (6)\end{matrix}$

FIG. 11 illustrates the operating principle of the first phase of thehybrid converter operating in both the buck mode and the auto mode inaccordance with various embodiments of the present disclosure. The buckmode operating principle of the hybrid converter 113 is similar to thatshown in FIG. 9 except that switch Q2 is turned off during the firstphase. It should be noted that during the first phase shown in FIG. 11,the charge pump capacitor C_(CP) is floating. In addition, the chargepump capacitor C_(CP) has been pre-charged to a voltage levelapproximately equal to twice the output voltage of the hybrid converter113. Such a pre-charged voltage helps to achieve a smooth transitionbetween the buck mode and the charge pump mode. In particular, thehybrid converter 113 can leave the buck mode and smoothly enter into thecharge pump mode if necessary.

FIG. 12 illustrates the operating principle of the second phase of thehybrid converter operating in both the buck mode and the auto mode inaccordance with various embodiments of the present disclosure. The buckmode operating principle of the hybrid converter 113 shown in FIG. 12 issimilar to that shown in FIG. 10 except that switch Q3 is turned offduring the second phase. It should be noted that during the secondphase, the charge pump capacitor C_(CP) is floating. In addition, thecharge pump capacitor C_(CP) has been pre-charged to a voltage levelapproximately equal to twice the output voltage of the hybrid converter113. Such a pre-charged voltage helps to achieve a smooth transitionbetween the buck mode and the charge pump mode because the charge pumpcapacitor C_(CP) has a voltage ready for the charge pump mode operation.Such a smooth transition between the buck mode and the charge pump modeis referred to as the auto mode throughout the description.

FIG. 13 illustrates the operating principle of the auto mode inaccordance with various embodiments of the present disclosure. Dependingon different input and output voltages, the hybrid converter 113 is ableto operate in one of the three operating modes when the auto mode isapplied to the hybrid converter 113. As shown in FIG. 13, there may betwo voltage thresholds, namely V_(TH1) and V_(TH2). V_(TH1) is greaterthan V_(TH2) as shown in FIG. 13. In some embodiments, VTH1 isapproximately equal to two times the output voltage of the hybridconverter 113 plus a hysteresis voltage (VHYST). VTH2 is approximatelyequal to two times the output voltage of the hybrid converter 113 minusthe hysteresis voltage (VHYST). In some embodiments, the hysteresisvoltage (VHYST) is about 5% of the output voltage of the hybridconverter 113. It should be noted that 5% of the output voltage ismerely an example. A person skilled in the art would understand thevalue of the hysteresis voltage (VHYST) may vary accordingly dependingon different applications and design needs.

In operation, when the input voltage of the hybrid converter 113 isgreater than V_(TH1), the hybrid converter 113 is configured to operatein the hybrid mode. The operation principle of the hybrid mode has beendescribed in detail above with respect to FIGS. 3-6, and hence is notdiscussed again. Under some operating conditions, the input voltage ofthe hybrid converter 113 falls into a range between V_(TH1) and V_(TH2),the hybrid converter 113 leaves the hybrid mode and enters into thecharge pump mode. The operation principle of the charge pump mode hasbeen described in detail above with respect to FIGS. 7-8. Furthermore,the input voltage of the hybrid converter 113 may drop below V_(TH2). Asshown in FIG. 13, the hybrid converter 113 leaves the charge pump modeand enters into the buck mode. The operation principle of the buck modehas been described in detail above with respect to FIGS. 10-11.

It should be noted that during an input voltage increase process, themode transition occurs in a similar manner. For example, when the inputvoltage increases and exceeds V_(TH2), the hybrid converter 113 leavesthe buck mode and enters into the charge pump mode. Likewise, when theinput voltage increases and exceeds V_(TH1), the hybrid converter 113leaves the charge pump mode and enters into the hybrid mode. Thedetailed mode transition process will be discussed below with respect toFIG. 14.

FIG. 14 illustrates the mode transition principle in accordance withvarious embodiments of the present disclosure. As shown in FIG. 14, themode transition between the hybrid mode and the charge pump mode occursat particular phases. When the hybrid converter 113 has a modetransition from the hybrid mode to the charge pump mode, the hybridconverter 113 leaves at the end of the fourth phase of the hybrid modeand enters into the first phase of the charge pump mode. On the otherhand, when the hybrid converter 113 has a mode transition from thecharge pump mode to the hybrid mode, the hybrid converter 113 leaves atthe end of the second phase of the charge pump mode and enters into thefirst phase of the hybrid mode.

FIG. 14 further illustrates the mode transition between the charge pumpmode and the buck mode. As shown in FIG. 14, when the hybrid converter113 has a mode transition from the charge pump mode to the buck mode,the hybrid converter 113 leaves at the end of the second phase of thecharge pump mode and enters into the first phase of the buck mode. Onthe other hand, when the hybrid converter 113 has a mode transition fromthe buck mode to the charge pump mode, the hybrid converter 113 leavesat the end of the second phase of the buck mode and enters into thefirst phase of the charge pump mode.

FIG. 15 illustrates a flow chart of applying a first control mechanismto the hybrid converter shown in FIG. 2 in accordance with variousembodiments of the present disclosure. This flowchart shown in FIG. 15is merely an example, which should not unduly limit the scope of theclaims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications. For example, various stepsillustrated in FIG. 15 may be added, removed, replaced, rearranged andrepeated.

Referring back to FIG. 2, the hybrid converter 113 comprises fourswitches Q1, Q2, Q3 and Q4. Depending on different operating parameters,the hybrid converter 113 may operate in three different operating modes,namely a hybrid mode, a charge pump mode and a buck mode. The hybridmode includes four operating phases; the charge pump mode includes twooperating phases; and the buck mode includes two operating phases. Inoperation, depending on design needs and different applications, thehybrid converter 113 may leave one operating mode and enter into adifferent operating mode. For example, the hybrid converter 113 mayfirst operate in the charge pump mode, and then enter into the hybridmode after the operating parameters have changed.

In some embodiments, the hybrid converter 113 may automatically switchfrom the charge pump mode to the hybrid mode when the output voltage ofthe hybrid converter 113 is greater than a predetermined voltagethreshold or is outside a predetermined output voltage range. Forexample, the hybrid converter 113 may leave the charge pump mode at anend of the first phase of the charge pump mode and enter into the hybridmode at a beginning of the second phase of the hybrid mode. Theoperating mode transition between the charge pump mode and the hybridmode is accomplished by the following steps.

At step 1502, the load and output voltage of the wireless power systemis detected by a suitable sensing apparatus or a plurality of sensingdevices. The detected load and voltage are processed by a controller. Inparticular, the detected load current and/or the output voltage arecompared with predetermined current and/or voltage thresholds or ranges.In some embodiments, the controller may be a digital controller.

At step 1504, the hybrid converter 113 is configured to operate in thecharge pump mode when the output voltage is within a predeterminedoutput voltage range and the load current is over a predeterminedcurrent threshold. The operation of the charge pump mode has beendescribed in detail above with respect to FIGS. 7-8.

It should be noted that the predetermined output voltage range is merelyan example, which should not unduly limit the scope of the claims. Oneof ordinary skill in the art would recognize many variations,alternatives, and modifications. For example, the input voltagetolerance of the load may be a factor in the process of determining theoperating mode of the hybrid converter 113.

At step 1506, the hybrid converter is configured to operate in thehybrid mode when the output voltage of the wireless power system isoutside the predetermined range and the load is greater than thepredetermined current threshold. In some embodiments, during theoperating mode transition, the hybrid converter 113 enters into a secondphase of the hybrid mode after finishing a first phase of the chargepump mode.

FIG. 16 illustrates a flow chart of applying a second control mechanismto the hybrid converter shown in FIG. 2 in accordance with variousembodiments of the present disclosure. This flowchart shown in FIG. 16is merely an example, which should not unduly limit the scope of theclaims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications. For example, various stepsillustrated in FIG. 16 may be added, removed, replaced, rearranged andrepeated.

The operating mode transition control mechanism shown in FIG. 16 issimilar to that shown in FIG. 15 except that the operating modetransition occurs at a different time. It should be noted that theoperating mode transition control mechanisms shown in FIGS. 15-16 may betaken individually or in combination to further improve the performanceof the hybrid converter 113.

At step 1602, the load and output voltage of the wireless power systemis detected by a suitable sensing apparatus or a plurality of sensingdevices. The detected load and voltage are processed by a controller. Inparticular, the detected load current is compared with predeterminedcurrent and/or voltage thresholds.

At step 1604, the hybrid converter 113 is configured to operate in thecharge pump mode when the output voltage is within a predetermined rangeand the load current is over a predetermined current threshold. Theoperation of the charge pump mode has been described in detail abovewith respect to FIGS. 7-8.

At step 1606, the hybrid converter 113 is configured to operate in thehybrid mode when the output voltage of the wireless power system isoutside the predetermined range and the load is greater than thepredetermined current threshold. In some embodiments, during theoperating mode transition, the hybrid converter 113 enters into thefourth phase of the hybrid mode after finishing the second phase of thecharge pump mode.

FIG. 17 illustrates a flow chart of applying a third control mechanismto the hybrid converter shown in FIG. 2 in accordance with variousembodiments of the present disclosure. This flowchart shown in FIG. 17is merely an example, which should not unduly limit the scope of theclaims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications. For example, various stepsillustrated in FIG. 17 may be added, removed, replaced, rearranged andrepeated.

At step 1702, the load and output voltage of the wireless power systemis detected by a suitable sensing apparatus or a plurality of sensingdevices. The detected load and voltage are processed by a controller. Inparticular, the detected load current and/or the detected output voltageare compared with predetermined current and/or voltage thresholds.

At step 1704, the hybrid converter 113 is configured to operate in thebuck mode when the load is less than a predetermined current threshold.The operation of the buck mode has been described in detail above withrespect to FIGS. 9-10.

FIG. 18 illustrates a flow chart of applying a fourth control mechanismto the hybrid converter shown in FIG. 2 in accordance with variousembodiments of the present disclosure. This flowchart shown in FIG. 18is merely an example, which should not unduly limit the scope of theclaims. One of ordinary skill in the art would recognize manyvariations, alternatives, and modifications. For example, various stepsillustrated in FIG. 18 may be added, removed, replaced, rearranged andrepeated.

At step 1802, the load and output voltage of the wireless power systemis detected by a suitable sensing apparatus or a plurality of sensingdevices. The detected load and voltage are processed by a controller. Inparticular, the detected load current is compared with predeterminedcurrent and/or voltage thresholds.

At step 1804, the hybrid converter 113 is configured to operate in thehybrid mode during a soft start process of the hybrid converter 113. Theoperation of the hybrid mode mode has been described in detail abovewith respect to FIGS. 3-6.

At step 1806, the hybrid converter 113 is configured to operate in thecharge pump mode after the soft start process finishes and the outputvoltage has been fully established. The mode transitions between thehybrid mode and the charge pump mode have been described above in detailwith respect to FIGS. 14-16, and hence are not discussed again to avoidunnecessary repetition.

It should be noted that the mode transition may occur during the softstart process. For example, the mode transition from the hybrid mode tothe charge pump mode may occur when the output voltage exceeds apredetermined value (e.g., 80% of the final output voltage).

Although embodiments of the present disclosure and its advantages havebeen described in detail, it should be understood that various changes,substitutions and alterations can be made herein without departing fromthe spirit and scope of the disclosure as defined by the appendedclaims.

Moreover, the scope of the present application is not intended to belimited to the particular embodiments of the process, machine,manufacture, composition of matter, means, methods and steps describedin the specification. As one of ordinary skill in the art will readilyappreciate from the disclosure of the present disclosure, processes,machines, manufacture, compositions of matter, means, methods, or steps,presently existing or later to be developed, that perform substantiallythe same function or achieve substantially the same result as thecorresponding embodiments described herein may be utilized according tothe present disclosure. Accordingly, the appended claims are intended toinclude within their scope such processes, machines, manufacture,compositions of matter, means, methods, or steps.

What is claimed is:
 1. A method comprising: configuring a hybridconverter to operate in a hybrid mode comprising four operating phasesin response to an input voltage of the hybrid converter greater than afirst threshold, wherein the hybrid converter comprises a capacitorconnected between a first switching node and a second switching node;configuring the hybrid converter to operate in a buck mode comprisingtwo operating phases in response to the input voltage of the hybridconverter less than a second threshold; and configuring the hybridconverter to operate in a charge pump mode comprising two operatingphases in response to the input voltage of the hybrid converter lessthan the first threshold and greater than the second threshold.
 2. Themethod of claim 1, wherein the hybrid converter comprises: a firstswitch, the capacitor and a second switch connected in series between anoutput of a power source and an inductor-capacitor filter; a thirdswitch connected between a common node of the first switch and thecapacitor, and a common node of the second switch and theinductor-capacitor filter; and a fourth switch connected between acommon node of the capacitor and the second switch, and ground, andwherein a common node of the first switch and the third switch is thefirst switching node, and a common node of the second switch and thefourth switch is the second switching node.
 3. The method of claim 2,wherein configuring the hybrid converter to operate in the hybrid modecomprises: in a first phase of the hybrid mode, configuring the firstswitch and the second switch to be turned on, and the third switch andthe fourth switch to be turned off; in a second phase of the hybridmode, configuring the second switch and the fourth switch to be turnedon, and the first switch and the third switch to be turned off; in athird phase of the hybrid mode, configuring the third switch and thefourth switch to be turned on, and the first switch and the secondswitch to be turned off; and in a fourth phase of the hybrid mode,configuring the second switch and the fourth switch to be turned on, andthe first switch and the third switch to be turned off.
 4. The method ofclaim 3, wherein configuring the hybrid converter to operate in thecharge pump mode comprises: in a first phase of the charge pump mode,configuring the first switch and the second switch to be turned on, andthe third switch and the fourth switch to be turned off; and in a secondphase of the charge pump mode, configuring the third switch and thefourth switch to be turned on, and the first switch and the secondswitch to be turned off.
 5. The method of claim 4, wherein: in responseto a mode transition from the hybrid mode to the charge pump mode, thehybrid converter leaves at the end of the fourth phase of the hybridmode and enters into the first phase of the charge pump mode; and inresponse to a mode transition from the charge pump mode to the hybridmode, the hybrid converter leaves at the end of the second phase of thecharge pump mode and enters into the first phase of the hybrid mode. 6.The method of claim 4, wherein configuring the hybrid converter tooperate in the buck mode comprises: in a first phase of the buck mode,configuring the first switch and the third switch to be turned on, andthe second switch and the fourth switch to be turned off; and in asecond phase of the buck mode, configuring the second switch and thefourth switch to be turned on, and the first switch and the third switchto be turned off.
 7. The method of claim 6, wherein: in response to amode transition from the charge pump mode to the buck mode, the hybridconverter leaves at the end of the second phase of the charge pump modeand enters into the first phase of the buck mode; and in response to amode transition from the buck mode to the charge pump mode, the hybridconverter leaves at the end of the second phase of the buck mode andenters into the first phase of the charge pump mode.
 8. The method ofclaim 6, wherein: in the buck mode, the capacitor is floating.
 9. Themethod of claim 6, wherein: in the buck mode, the capacitor ispre-charged to a voltage level approximately equal to twice an outputvoltage of the hybrid converter.
 10. The method of claim 9, furthercomprising: pre-charging the capacitor to the voltage level forachieving a smooth transition between the buck mode and the charge pumpmode.
 11. The method of claim 1, wherein: the first threshold isapproximately equal to two times an output voltage of the hybridconverter plus a hysteresis voltage; and the second threshold isapproximately equal to two times the output voltage of the hybridconverter minus the hysteresis voltage.
 12. The method of claim 11,wherein: the hysteresis voltage is about 5% of the output voltage of thehybrid converter.
 13. A method comprising: detecting an input voltageand an output voltage of a power system comprising a hybrid converter,wherein the hybrid converter comprises a capacitor connected between twoswitching nodes of the hybrid converter; configuring the hybridconverter to operate in a hybrid mode comprising four operating phaseswhen the input voltage of the hybrid converter is greater than a firstthreshold; configuring the hybrid converter to operate in a buck modecomprising two operating phases when the input voltage of the hybridconverter is less than a second threshold; and configuring the hybridconverter to operate in a charge pump mode comprising two operatingphases when the input voltage of the hybrid converter is between thefirst threshold and the second threshold.
 14. The method of claim 13,wherein the power system is a wireless power transfer system comprising:a transmitter switching network coupled to an input power source; atransmitter coil coupled to the transmitter switching network; areceiver coil configured to be magnetically coupled to the transmittercoil; a rectifier connected to the receiver coil; and the hybridconverter connected between the rectifier and a load.
 15. The method ofclaim 13, wherein the hybrid converter comprises: a first switch, thecapacitor and a second switch connected in series between an output of apower source and an output filter; a third switch connected between acommon node of the first switch and the capacitor, and a common node ofthe second switch and the output filter; and a fourth switch connectedbetween a common node of the capacitor and the second switch, andground.
 16. The method of claim 15, wherein configuring the hybridconverter to operate in the hybrid mode comprises: in a first phase ofthe hybrid mode, turning on the first switch and the second switch, andturning off the third switch and the fourth switch; in a second phase ofthe hybrid mode, turning on the second switch and the fourth switch, andturning off the first switch and the third switch; in a third phase ofthe hybrid mode, turning on the third switch and the fourth switch, andturning off the first switch and the second switch; and in a fourthphase of the hybrid mode, turning on the second switch and the fourthswitch, and turning off the first switch and the third switch.
 17. Themethod of claim 15, wherein configuring the hybrid converter to operatein the charge pump mode comprises: in a first phase of the charge pumpmode, turning on the first switch and the second switch, and turning offthe third switch and the fourth switch; and in a second phase of thecharge pump mode, turning on the third switch and the fourth switch, andturning off the first switch and the second switch.
 18. The method ofclaim 15, wherein configuring the hybrid converter to operate in thebuck mode comprises: in a first phase of the buck mode, turning on thefirst switch and the third switch, and turning off the second switch andthe fourth switch; and in a second phase of the buck mode, turning onthe second switch and the fourth switch, and turning off the firstswitch and the third switch.
 19. The method of claim 15, whereinconfiguring the hybrid converter to operate in the buck mode comprises:in a first phase of the buck mode, turning on the first switch, thesecond switch and the third switch, and turning off the fourth switch;and in a second phase of the buck mode, turning on the second switch,the third switch and the fourth switch, and turning off the firstswitch.
 20. The method of claim 13, wherein: the first threshold isapproximately equal to two times an output voltage of the hybridconverter plus a hysteresis voltage; and the second threshold isapproximately equal to two times the output voltage of the hybridconverter minus the hysteresis voltage.